RFC 5942, "IPv6 Subnet Model: The Relationship between Links and Subnet Prefixes", July 2010Source of RFC: 6man (int)
Errata ID: 6417
Publication Format(s) : TEXT
Reported By: Ted Lemon
Date Reported: 2021-01-29
Section 4 says:
In bullet item 4, the behavior for hosts when the default router list is empty is specified in a way that means that no prefix can ever be considered on-link. 4.b says that address resolution (which I take to mean neighbor discovery) should not be performed for any non-link-local address. It is entirely possible for an on-link, non-default router to advertise an on-link prefix. In this case, the prefix should be considered on-link, and address resolution should be permitted. I don't see a way to read the text to allow this.
It should say:
I think the confusion is in 4.b, which should read: The host MUST NOT perform address resolution for non-link-local addresses that are not known to be on-link as described in section 3, part 1.
I don't know if the problem is that "non-link-local" should have been "non-on-link" or if the authors just weren't taking RFC4191 into consideration, but in the presence of RFC4191, requiring a default router before a prefix can be considered on-link renders perfectly valid configurations non-functional.